






^*^'J^^'\ /.c;^-% /.-^i-X <? >'^Mk °- 









^"-^^' 


















^^ ^ ' " ^ ^^. 



'^l 
















4 O 







\/ 























<^ aP 'w^- ^ "^ 















^. 



(: 



-'. 3 4 '^ 



;^¥ 




<yf GRAIN DUSTS 



• estimation t.y 

Mill«rfl' Committee of Buffalo^ N. V 
Under tKe Direc- 
Dr. Ge orge A . Hulett , ijh itf (Jhttm ist 
US. Bureau al Min- 



A PRELIMINARY REPORT 

David J. Price 
HaroH H. Browr 




PITTSBURGH. PA. 



EXPLOSIBILITY 
of GRAIN DUSTS 



Cooperative Investigation by 

Millers' Committee of Buffalo, N. Y. 

Unaer tne Direction or 

Dr. George A. riulett, Cnief Cnemist 

U. S. Bureau or Mines 



A PRELIMINARY REPORT 

by 
David J. Price 

ana 
Harola H. Brown 



PITTSBURGH, PA. 
JULY, 1914 



rs 



THE MILLERS' COMMITTEE OF BUFFALO, N. Y. 



LAWRENCE E. HARMON, CUirman, 

President, Burralo Cereal Company 

FRANK F. HENRY, 

Manager, Wasnourn-CrosDy Company 

GEORGE F. URBAN, 

Secretary, George Urban Milling Company 



^<_ M- ' 



The Exploslbility of Grain Dusts 



A PRELIMINARY REPORT 
By David J. Price and Harold H. Brown 




GENERAL INTRODUCTORY STATEMENT 

UCH attention has been given to the study of the 
inflammability of various forms of carbonaceous dusts 
in this country and abroad, in recent years. Prelim- 
inary conclusions indicate that under certain favorable 
conditions nearly all forms of carbonaceous dusts are explosive. 
Many disastrous explosions have occurred in bituminous coal 
mines throughout the United States and European countries, 
where firedamp or "methane gas" had not been ordinarily 
detected. The cause of these explosions has been traced to the 
ignition of coal dust that propagated to a violent explosion 
throughout the entire mine, causing great loss of life and consid- 
erable property damage. The large loss of life that usually 
accompanies a mine disaster of this nature brings coal-dust 
explosions forcibly to our attention at the time of the occurrence. 
We must not conclude, however, that coal dust is the only kind of 
dust that will explode, as experiments have clearly shown that the 
dusts of other substances containing carbon are explosive. In 
these various forms of carbonaceous dusts are included the dusts 
produced in most of the industries in which grain or its products 
are used. The object of this preliminary report is to briefly sum- 
marize the various conditions under which explosions of this 
nature have occurred, and to give a series of results already 
obtained relative to the exploslbility of these dusts. 

ORIGIN OF THE STUDY 

I.- 
Although many men prominently identified with the milling 

industry accept the theory that carbonaceous dusts are explosive, 

others feel that their plants are not in danger except when only 



The Explosibility of Grain Dusts 



certain kinds of dusts are produced. Explosions in several flour 
mills in 1878, clearly proved that flour dust under certain condi- 
tions is highly explosive, and immediately caused flour millers to 
take precautions to guard against a repetition of an occurrence 
of this nature. 

General interest was again awakened among milling men, 
however, when an explosion occurred in a feed-grinding plant at 
Buffalo, N. Y., on June 24, 1913, by which 33 men lost their lives, 
and upwards of 70 were injured. To assist in the work being done 
upon the explosibility of coal dust, the Bureau of Mines, for some 
time has endeavored to study dust explosions in surface plants, 
and therefore made inquiry into this disaster. The Bureau in 
this way came into touch with the officials of the various milling 
companies in that section. The cereal, flour and feed millers of 
Buffalo and Western New York were desirous of obtaining any 
possible information relative to the explosibility of grain dusts, 
that would assist them in taking effective safety precautions, in 
addition to the measures that had already been adopted. 

A co-operative movement between milling interests gener- 
ally and the Bureau of Mines, was arranged for the purpose of 
making a scientific study of the explosibility of grain dusts, and 
of methods pertaining to the prevention of such explosions. The 
Millers were represented in the conduct of the work by Messrs. 
Lawrence E. Harmon, President of Buffalo Cereal Company; 
Frank F. Henry, Manager, Washburn Crosby Company, and 
George F. Urban, Secretary of George Urban Milling Company, all 
of Buffalo, N. Y. Prof. George A. Hulett, Chief Chemist of the 
Bureau of Mines, was placed in charge of the study, and David J. 
Price was assigned to the field engineering work in connection 
with the problem. The work was started August 1, 1913, and a 
complete series of dust samples was collected, covering the vari- 
ous lines of milling, in order to conduct the necessary tests to 
determine the degree of inflammability. The aim was to trace 
the grain from the beginning of the handling, either from boats 
or cars, through the various points in the elevators, and the 
different stages of production, thereby securing a representative 
series of dust samples throughout the entire plant. These were 
carefully collected, and the conditions at the points of collection 
were fully noted, relative to nature of dust, manner of production, 
quantity present, and similar essential details. On February 1, 



Extent of Grain Industry 




1914, Dr. H. H, Brown was assigned to the laboratory study of 
these dusts, relative to their chemical nature and degree of 
inflammability. 

EXTENT OF GRAIN INDUSTRY 
Flour and Feed Mills 

' T WILL be of interest to note the extent of the grain 
industry, and the number of milling plants included 
in a study of this nature. The census report for 1909, 
relating to the milling industry in the United States, 
incluaecl all mills grinding wheat, rye and buckwheat, corn for 
hominy, grits or feed, but not mills doing exclusively a custom 
business, or factories making fancy cereal food or other special 
food preparations as a chief product. It will be of interest to note, 
however, that the figures make milling the fifth in rank in the 
United States. The report shows that in 1909 there were 11,691 
establishments in this country, with a total number of 66,054 
persons engaged.* 

The following table (from Vol. X, Thirteenth Census, U. S., 
pp. 407 and 420) shows some very interesting statistics regarding 
the industry: 

. 1909 ^ 

Number of establishments 11,691 

Persons engaged in the industry 66,054 

Primary horsepower 853,584 

Capital invested $349,151,779 

Expenses 827,522,349 

Salaries and wages 33,981,153 

Cost of materials used 767,576,479 

Miscellaneous expenses 25,964,717 

Value of products 883,584,405 

Value added by manufacture 116.007,926 

Grain ground, bushels 800,247,961 

In the total number of establishments as given above, there 
were 5,621 mills that used over 491,000,000 bushels of wheat, 
producing more than 105,000,000 barrels of flour, with a value 
exceeding $546,000,000. 



•From the Millers' Almanack, for 1914-1915, page 83, published by The 
Northwestern Miller, Minneapolis, Minn. 



The Explosibility of Grain Dusts 



There were 2,529 mills manufacturing chiefly feed for live 
stock, and grinding the following quantity of grain : 

Corn 42,442,263 bushels 

Oats 14,414,992 bushels 

Other grain 13,376,825 bushels 

These mills produced 1,715,899 tons of feed, valued at 
$48,242,782. The value of all other products was $2,551,259. 

Glucose and Starch Industry'-' 

r— 1909 N 

Number of establishments 118 

Persons engaged in the industry 5,827 

Primary horsepower 28,257 

Capital invested $38,866,419 

Expenses 43,973,558 

Salaries and wages 4,079,722 

Cost of materials used 36,898,771 

Miscellaneous expenses 2,995,065 

Value of products 48,799,311 

Value added by manufacture 11,900,540 

The above statistics will be of interest in classifying the 
various dust explosions according to the industries in which they 
have occurred. Reference to the tabulated form that follows, 
showing nature and location of explosions since 1905, makes a 
comparison possible. 

INVESTIGATIONS OF RECENT EXPLOSIONS 

iNE OF the early steps taken at the beginning of the 
study was an effort to secure data relative to occur- 
rences of this nature in the United States and 
European countries, in order, if possible, to assist in 
establishing the various sources of origin, and conditions under 
which these explosions occur. Early investigations indicated 
that a large number of explosions have occurred in grain and 
cereal mills throughout this country and abroad, with varying 
degrees of violence and damage. Owing to the recognized 
advances in milling equipment and construction in recent years, 
it was thought advisable to devote the early part of the study to 
the explosions that have taken place in modern plants, equipped 

*Prom Vol. X, Thirteenth Census United States, page 429. 




Investigations of Recent Explosions 



with improved milling devices and lighting systems. For this 
reason the reported occurrences of this nature since 1905 were 
especially investigated and carefully studied. It was thought 
that explosions occurring since this date would include plants 
that had taken advantage of improved milling equipment, and 
where n£cessary provisions were being taken for dust collecting 
and handling. 

Frequency of Explosions 

Explosions in grain mills were rather frequent, both in this 
country and abroad, prior to the early '80s, as a result of which 
it was discovered that the methods of dust collecting were not 
efficient, and new systems accordingly were introduced. At the 
time of these occurrences the old "stive" or "dust room'' was in 
general use, and the dust produced during the milling process 
was collected in this chamber. This provision made it possible 
at all times for a dangerous amount of dust to be in suspension, 
that would produce a violent explosion upon ignition. 

The old "stive" or dust room has been replaced by dust- 
collecting systems of various types and construction. In the 
present modern systems of collection the dust is carried through 
pipe lines from the different points of production by means of air 
currents produced by an operating fan, to the dust collector, 
where the separation takes place. 

The danger due to the old "stive" or dust room was well 
proven by explosions in Minnesota in 1878, and in Illinois in 1893. 
In both cases very violent explosions occurred in flour mills where 
the dust was carried to a chamber of this nature. The former 
explosion caused the loss of 18 lives and extensive damage to 
property; the other explosion occurred at night during a fire. 
The mill was completely destroyed and considerable damage was 
done to surrounding property. 

Most milling plants throughout the country have taken 
advantage of the improved systems of dust collection, and the 
old "stive" room is obsolete in modern mills. However, it would 
appear that in some of the European countries advances along 
this line were not so rapid as in this country. An explosion of 
considerable magnitude is reported as occurring in Liverpool as 
late as the spring of 1905, in a flour mill where a dust chamber 
or "stive" room was in use. It is thought the explosion, which 
was followed by a disastrous fire, originated in this dust chamber. 



8 The Explosibility of Grain Dusts 

It has been observed that the majority of explosions in 
more recent years have occurred in mills handling or grinding 
coarse grain. By the term "coarse grain" is meant grain such 
as oats, corn, etc., other than wheat; and mills grinding grain 
of this nature are termed "coarse grain mills," to distinguish 
them from flour mills. A number of explosions in plants of this 
nature have taken place within the last ten years, causing in some 
cases a large loss of life and complete destruction of property. 

There is given in the following table a list of grain-dust 
explosions that have occurred in the United States since 1905, 
which thus far have been investigated: 



Investigations of Recent Explosions 




10 The Explosibility of Grain Dusts 

EXPLOSIONS IN THE UNITED STATES 
Explosion and Fire in Iowa 

CEREAL mill in Iowa was extensively damaged by fire 

A\ on March 5, 1905. The fire is thought to have followed 
ft- an explosion, reported to have originated underneath 
a grinding machine. Two employes lost their lives, 
and the property was completely destroyed. The fire seems to 
have started from an attrition mill which was grinding oat hulls. 
It was thought that the mill produced sufficient sparks to cause an 
ignition of the dust cloud within the grinding machine. One of 
the mill attendants heard a hard substance strike the plates 
about the time of the occurrence. An explosion took place in the 
conveyor line under this machine, and traveled along the conveyor 
to an adjoining elevator leg, and thence into a storage bin. The 
elevator leg was blown out, and a very disastrous fire followed. 
The estimated property loss is one of the largest on record. 

Explosion in Vermont, 1908 

On October 7, 1908, an explosion occurred in an elevator in 
Northern Vermont. Fifteen employes were killed, and two women 
who were walking on the railroad tracks outside of the plant were 
so badly burned that they died soon afterward. Fire followed 
the explosion, and the property was very badly damaged. 

This elevator was used by its operators as a feed mixing 
plant; that is, the feed was ground, or prepared for mixing at 
another point, and sent in cars to the elevator, where it was 
unloaded and mixed. We can, therefore, class this as an "elevator 
explosion," and at the same time we are forced to conclude that 
if an explosion with such terrible force and violence could occur 
at this elevator, that the grain elevators of the country are at all 
times subject to the possibility of a similar occurrence if favor- 
able conditions exist. Many milling men have maintained a false 
sense of security in recent years, and have felt that the elevators 
were not especially a source of danger; and that as long as an 
explosion did not originate in the grinding mill proper, they were 
reasonably safe. This would also seem to indicate the belief that 
an explosion could not occur in an elevator at a plant where no 
milling or grinding was being done. This explosion alone would 
seem to indicate sufficiently that the dusts created during the 



Explosions in the United States 11 

elevating and storing of grain are explosive and dangerous. Other 
explosions in elevators prior to 1908 have occurred from time to 
time, and are matters of record. 

Explosion in Illinois, 1910 

An explosion occurred in the elevator building of a glucose 
factory in Illinois, on August 7, 1910, as a result of which two men 
were killed and seven injured. The material that exploded was a 
light pulverized powder called "gluten feed," which is manufac- 
tured from corn by the removal of starch, oil, etc., and was sold 
as cattle feed. The corn was first soaked in water for a period of 
about 48 hours, and then delivered to a grinding mill, in which 
it was cracked, causing the removal of the germ, which floated off 
in a body of starchy water. The corn was then still further 
ground in stone mills and washed in several reels and shakers in 
order to separate out the starch for the manufacture of glucose. 
The material that remained was gluten, which was delivered wet 
to the filter presses, which reduced the moisture content to about 
50 per cent. It was then dried in a rotary steam drier to about 
12 per cent, moisture, after which it was further ground in an 
attrition mill. The gluten feed was taken from the attrition mill 
to a separate building, called the feed elevator, by means of an 
air draft operating through a 16-inch galvanized iron spout about 
375 feet long, and carrying the gluten 140 feet in elevation. The 
air draft was maintained by a 70-inch planing mill exhaust fan, 
driven 1,500 revolutions by a belt connected, 35-horse power 
electric motor. This fan was located about ten feet from the 
attrition mill, and delivered about 25 pounds of air for each 
pound of gluten carried. The spout delivered its burden to a 
"cyclone collector" on top of the elevator building. 

The evidence at hand after the explosion led to the belief that 
the cause of the explosion was a stream of sparks emanating 
from the plates of the attrition mill, which was traveling at 1,500 
revolutions per minute. These sparks were thought to have been 
caused either by a momentary clogging of the feed of the mill, 
which would allow the grinding plates to rub against each other, 
or by a piece of foreign material striking against the plates. A 
smouldering fire having originated between the mill plates, the 
strong air draft quickly fanned it into a blaze. The amount and 
coarseness of the gluten probably prevented an explosion in the 
delivery pipe, but the blaze and the pressure of the resulting 



12 The Explosibility of Grain Dusts 

gases increased enormously. When this fire and force reached 
the elevator building enough dust was jarred into the air to make 
favorable conditions for the explosion which followed. This 
explosion clearly shows that the greatest violence was at a point 
some distance away from the point of origin. Although the 
source of origin was not in the elevator, the conditions were such 
that when the flame and pressure reached this point the ignition 
of the dust thrown in suspension produced a violent explosion. 

Explosion in Western New York, January, 1910 

An explosion occurred in a cereal mill in Western New York 
on January 4, 1910. As a result of the fire which followed the 
explosion several men were killed, and the plant badly damaged. 
The explosion occurred at night, when there were only a limited 
number of men at work. There had been a few days' suspension 
of work for the purpose of taking an inventory, and the plant had 
been cleaned generally throughout, the dust having been swept 
up and removed. The weather was very cold, the temperature 
being below zero. The cause of the explosion has never been 
definitely determined, owing to the complete burning of that 
section of the plant in which it occurred. 

Explosion in Indiana, 1910 

An explosion occurred in a starch factory in Indiana on 
March 7, 1910, accompanied by much violence and property 
damage. One of the causes of the original ignition is thought to 
have been a fire that originated in the starch kiln house tunnels. 
According to this theory, a piece of burning waste, or other 
burning matter, was blown into these drying tunnels through the 
medium of the large fan blowers (forcing air through large coils 
of steam heater piping into the tunnels) , This burning substance 
is supposed to have come in contact with some re-dried starch and 
immediately ignited the same. The fire which started in this 
manner spread into four of the tunnels, and the combustion was 
so rapid and the heat so intense that a number of employes were 
very severly burned. Owing to the presence of the fine dry starch 
dust, the fire spread through a conveying system to an adjoining 
building, which was destroyed. 

Another theory advanced relative to this explosion was that 
the point of origin was in the starch grinding house, and that the 



Explosions in the United States 13 

flame was transmitted to the adjoining building by means of the 
conveyor lines. This is made possible by the fact that any hard 
substance or foreign material, striking against the revolving arms 
or plates on the interior of the grinding machine, might produce a 
series of sparks that would cause an ignition of the starch dust 
cloud on the interior of the machine. The type of machine in use 
consisted of a series of arms or beaters mounted onto a revolving 
shaft or runner head that revolved at a very high rate of speed. 
It was thought that a series of sparks produced in this manner 
caused a fire in the conveyor line, that propagated to a very disas- 
trous explosion. In this respect the traveling of the explosive 
wave for some distance from the point of origin to the point where 
the greatest damage was done resembles an explosion already 
referred to above. It would seem to indicate that the initial 
point of ignition is not always where the greatest amount of 
damage is done, and also that at the point of ignition there may 
be indications of very little damage. 

Explosion in Illinois, 1912 

An explosion occurred in a starch factory in Illinois on 
November 25, 1912, and was accompanied by a large loss of life, 
and complete loss of property. The general opinion relative to the 
origin of this explosion seems to be that it started in the starch 
drying house. The dust is usually very fine and dry, and when 
in suspension in the air in sufficient quantity produces a dan- 
gerous condition. The exact cause has been a matter of conjec- 
ture, and owing to the workmen being killed was probably never 
definitely determined. The possibility of one of the men igniting 
the dust cloud by striking a match, was advanced. The explosion 
is described as being terrific in nature, and the effect was felt 
for some distance from the plant. 

Explosion in Western New York, June, 1913 

The most violent explosion of grain and cereal dusts in this 
country in recent years occurred in a feed-grinding plant in 
Western New York on June 24, 1913. The explosion was followed 
by a very disastrous fire, which destroyed and damaged property 
for some distance away. There were 33 lives lost as a result 
of the explosion and upwards of 70 people injured. The explosion 
occurred in the afternoon, about 4 o'clock, on a very warm, sultry 
day, with the temperature about 90 degrees, and the humidity 



14 The Explosibility of Grain Dusts 

about 74 per cent. This reading, however, was obtained by the 
United States Weather Bureau, some distance away from the 
plant, and may not represent the humidity conditions at the mill. 
When the explosion occurred, the mill was in the regular process 
of operation, engaged in the production of feeds. The explosion 
is described as consisting of two reports, one following the other, 
with the second report louder than the first. Numerous theories 
have been advanced relative to the origin of the explosion, but 
the exact cause will probably never be determined definitely. An 
inquest of extended sessions was conducted by the City Court, 
with an effort to determine the cause and circumstances of the 
explosion. The decision of the Court, after examining 110 wit- 
nesses, many of whom were employes, was that "the testimony, 
without exception, has been that the plant on that day was in 
good working order, and that all ordinary precautions for the 
protection of the men had been taken. No evidence has been 
produced that would throw any light upon the cause of the acci- 
dent, and I therefore find that the men whose deaths were caused 
by that accident, came to their deaths from fire originating from 
causes unknown." 

Explosion in Iowa, September, 1913 

An explosion occurred on the night of September 11, 1913, 
in a cereal mill in Iowa. Fortunately no lives were lost, but the 
property was considerably damaged by the explosion and the fire 
which followed. The explosion occurred in a section of the plant 
where oat hulls were being ground for feed, and the greatest 
damage was done in this section. The explosion was charac- 
terized by a sudden puff, or report, followed by a body of flame 
and fire. The conveyor lines from the grinding machine to the 
storage bins gave evidence of fire, and the explosive wave seemed 
to travel through this part of the plant. Although the grain is 
said to have been reasonably clean, it is thought that some foreign 
material may have been introduced into the grinding machine, 
producing sparks sufficient to ignite the dust cloud present. The 
flame thus produced traveled along the conveyor lines and elevator 
legs until the receiving bins or hoppers were reached, when the 
explosion occurred. 

Accident in Western New York, September, 1913 

On September 13, 1913, an accident occurred in a feed mifl 
in Western New York. The occurrence cannot be considered as 



Explosions in the United States 15 

a complete explosion, but rather a series of inflammations of dust 
with limited explosive force and violence. Fire was discovered 
in one of the conveyor lines under the fourth floor of the building, 
and repeated efforts were made to prevent the spreading of the 
flames. A few hours after fire was first discovered the flames 
broke out with much force and violence, and considerably dam- 
aged the property. For some time preceding the accident it is 
thought trouble had been experienced with foreign material 
entering the grinding machines, and it is supposed the original 
sparks that ignited the dust were produced in this manner. It 
would appear, however, that the presence of inflammable dust 
increased the spread of the flames, and added to the extent of 
damage and violence. 

Explosion in Kansas, November, 1913 

A slight explosion occurred in a flour mill in Kansas in 
November, 1913. The explosion was of limited proportions, and 
there was no loss of life involved nor extensive property damage 
done. The occurrence took place about two weeks after an 
attrition mill had been installed for grinding wheat screenings. 
The mill was installed with a metal bin directly under the grinding 
machine, discharging the ground material into this bin, conveying 
the same from this bin to the elevator boot. At the time of the 
explosion there was not sufficient dust present to cause serious 
damage, and the only damage done was a bulging out and loosen- 
ing of the sides of this metal bin. The explosion made a very loud 
report and filled the mill with smoke. This occurrence would 
indicate that a grinding machine of this nature should not dis- 
charge directly into a bin unless provision is made in some manner 
for excessive pressure produced in case of an ignition of dust. 

Explosion in Iowa, November, 1913 

An explosion took place in a cereal mill in Iowa on November 
6, 1913. Two men were very badly burned and the property 
suffered considerable damage as a result of the accident. The 
explosion occurred during the noon hour, when most of the 
employes were outside the plant. The tender at the attrition 
mill was sitting near the machine, eating lunch, when he heard 
an explosion inside the machine. The explosion is described as 
being light in nature, and was followed by a later explosion of a 
loud, rumbling nature, that shook the entire plant. The flames 



16 The Explosibility of Grain Dusts 

were carried by means of conveyor lines and elevator legs up into 
a large storage bin. This bin contained only a small amount of 
ground material, and was almost empty at the time. The flames, 
upon reaching the bin, ignited the dust in suspension, thereby 
producing the violent explosion which followed. 

Explosion in Ohio, December, 1913 

An explosion occurred early in December, 1913, in an elevator, 
in Ohio. There were no lives lost, and the damage to the property 
was limited. However, the fact that the explosion occurred in 
an elevator leg, during the transfer of grain, at a point in the 
elevator building where there was no grinding machinery, would 
indicate that grain elevators, as well as milling plants, may be 
subject to explosions of dust produced in the process of trans- 
ferring and elevating grain under normal conditions. 

The explosion occurred in an elevator leg used for taking 
grain from one bin and transferring to another. The leg con- 
tained 178 buckets, 12 inches apart, and projecting 6 inches from 
the belt. The size of the leg was 18 inches by 9 inches on the 
outside, and the buckets were running about 471 feet per minute. 
This elevator leg was situated in the middle of the elevator 
building, about 20 feet from the front. It is thought the explo- 
sion occurred in or near the first floor of the elevator. The foot of 
the elevator extended down into the sub-basement, but there did 
not seem to be any evidence of explosion at that point. The foot 
was intact, the dust was not disturbed in the foot, or the conveyor 
running into the foot. The leg on the first floor was blown olf, 
and the head at the top of the elevator was blown apart. After 
the explosion occurred there was an odor present that resembled 
the odor following the discharge of a shotgun. This was quite 
noticeable on the first floor, and on the top of the elevator where 
the flames escaped. The officials concluded that it was possible a 
loaded cartridge had become mixed with the grain in shipment, 
and due to the friction in handling, was exploded, and ignited 
the dust. 

At the time of the explosion one of the men was using an 
extension light cord, with an incandescent bulb attached, to look 
into the leg through an opening on the first floor. This examina- 
tion was being made at the time the explosion occurred, and later 
it was found that the extension had been burned out. It was not 



Recent Explosions in Europe 17 

definitely determined what relation this had to the explosion, but 
suggests the possibility of an ignition of a dust cloud of this 
nature by an electric spark. This occurrence in Ohio, with others 
of its kind, indicates that the dusts arising from the handling of 
grain, such as oats, corn, wheat, etc., are of a highly explosive 
nature. An opinion exists among some elevator owners that the 
only dangerous dusts are those produced during the grinding and 
milling processes. They base this belief on the fact that grain 
coming from the field would be mixed with sufficient incom- 
bustible material to render the dust produced somewhat inert, 
and therefore not explosive. The dusts, no doubt, contain a large 
quantity of field dirt, but the dust coming from the husks or 
shells of the grain mixes in very large proportions with the field 
dust already present, and the mixture in this way is made inflam- 
mable. The large number of explosions of this nature in grain 
elevators where there is no grinding done, proves very clearly 
that an explosion may occur under certain favorable conditions. 

Explosion in Texas, March, 1914. 

An explosion occurred in an elevator in Texas in March, 1914. 
The report of the explosion is described as resembling a muffled 
roar, similar to that of a heavy gun fired within the building. 
Fortunately no one was hurt, but the force of the explosion was 
sufficient to blow out the sides of the spouting floor of the 
building. It is another example of the possibility of an explosion 
of elevator dusts. 



RECENT EXPLOSIONS IN EUROPE 
Explosion at Glasgow, Scotland, November, 1911 

N EXPLOSION occurred in a provender mill, grinding 

Au) peas, beans and wheat, at Glasgow, Scotland, on 
\^ November 10, 1911. As a result of this explosion two 
men employed by the firm, and three children who 
were passing along the street at the time of the accident, were 
killed, and eight persons were injured. The explosion seems to 
have been caused by dust, which had accumulated on an overhead 
beam, being dislodged and falling upon the open flame of a 
Bunsen burner. The operations carried out in this factory con- 
sisted in grinding peas, beans and wheat. At the time of the 
explosion all the millstones, except those used for grinding 



18 The Explosibility of Grain Dusts 



wheat, were running. The accident occurred at about 6:30 P. M., 
and the work was being carried on by artificial light. The mill 
was lighted by naked gas jets, and though most of these were in 
fairly safe positions, a light of a portable nature appears to have 
been placed in a spot where dust could have fallen on it. The 
explosion clearly indicates that a disastrous explosion may be 
produced by an open gas jet, in a plant where dust of this nature 
is produced. 

Explosion at Liverpool, 1911 

Probably the most disastrous explosion on record, as far as 
loss of life is concerned, occurred in a linseed mill in Liverpool, 
England, on November 24, 1911. As a result of this explosion 
39 persons were killed, and 101 were injured. The explosion was 
thought to have originated in the basement of the plant, where six 
large disintegrators for grinding oil cakes, beans and other mate- 
rials, and the necessary elevators, were at work. It was consid- 
ered to be due to the ignition of a dense cloud of dust produced 
by the breaking of a driving belt on one of the machines. This 
belt was six inches wide, and ran at a speed of about 5,000 feet 
per minute, and it was said that when one of these belts broke a 
fog of dust was raised owing to the disturbance of dust on the 
girders in the room. The definite cause of the ignition of the 
dust cloud which was raised was not fully determined, and is only 
a matter of conjecture. Experiments conducted with samples 
of the dust collected from the tops of pipes and wall ledges 
showed that an explosion of a dense cloud of such dust could be 
caused by: 

(1) The ignition of a match; 

(2) Contact with a naked gas flame ; 

(3) The flash caused by fusing of an electric wire; 

(4) Sparks produced by breaking circuit of an electric 
magnet. 

This latter test was carried out because the disintegrators 
were fitted with electro-magnetic separators. There were no 
lighted gas jets in that part of the works affected, and there did 
not seem to be any direct evidence of the burning of matches. 
Of the two remaining possible causes, the inspector concluded 
that the burning of a fuse on a temporary switchboard for light 
installation, provided the flame necessary for the ignition of the 
dust. Although this cause cannot be definitely assigned, it indi- 



Summary of Explosions 19 



cates that we can derive valuable conclusions from this occur 
rence relative to the relation of the dust cloud and electric sparks. 

Explosions at Manchester, England, 1911 and 1913 

Two explosions that appear to be somewhat similar in nature, 
occurred in a dextrine works at Manchester, England, on March 
21, 1911, and March 11, 1913. In the first explosion three men 
were killed, and five others injured. As a result of the second 
explosion eight men were injured, of whom three subsequently 
died. The operators carried on the manufacture of dextrine 
(British gum). Starch, ordinary flour, and a small quantity of 
hydrochloric and nitric acids were the only substances used. The 
inspectors in charge of the investigation concluded that the dust 
explosions in both occurrences originated in the same manner. 
It is thought that an ignition of dust was produced inside the fan 
casing that was forcing the hot air to the drying stoves located 
in the end of the plant. This ignition in the fan occurred as 
follows: A small accumulation of dust being dislodged, possibly 
from the beam supporting the fan, dropped onto an open gas jet 
about tWo feet below the beam, and was ignited. This flame was 
drawn into the fan casing, either through a badly fitting inspec- 
tion door in the air inlet duct, or through the openings in that 
duct, which fitted badly at its junction with the casing of the fan. 
The flame thus produced was driven along the hot air duct, setting 
up an explosive wave within the duct, which finally exploded the 
contents of the drying stoves, either by firing directly the dust 
at the bottom of the stoves, or by causing the evolution of inflam- 
mable gases (by destructive distillation of the dust on the trays 
and racks), which were fired by the flame and immediately pro- 
pagated an explosion. A series of tests of samples of dust 
collected at this plant on the day following the explosion, showed 
that all the samples collected were highly inflammable, and when 
in suspension in the air were capable of propagating or spreading 
the flame very rapidly. 

SUMMARY OF EXPLOSIONS 

Y^'^YHE PRELIMINARY work in the study of grain 
"V 7|T X dust explosions, as already stated, has been de- 
j\ fii ^^^^^ ^^ ^^^ explosions occurring in more recent 

0^<&«5 years. It will be observed that a large number of 
explosions of this nature have occurred during the last ten years 
in this country and abroad. The summary obtained up to the 



20 The Explosibility of Grain Dusts 

present time indicates that at least thirteen of these explosions 
have occurred in the United States since 1905, and of the number 
stated, six have occurred since the explosion in Western New York 
in June, 1913. This would seem to indicate that a larger number 
of explosions may have occurred during the ten-year period than 
already enumerated, but have not been a matter of record. The 
fact that this study began August 1, 1913, explains the complete 
record of these occurrences during the last year. The explosions 
noted in this country have occurred in plants that were consid- 
ered modern, and where advantage was taken of modern milling 
ideas and improved mechanical devices. The explosions have not 
been traced to carelessness in any case, but the indications are 
that they probably have taken place under unusual conditions. 
For this reason it may safely be concluded that a much larger 
number than the thirteen explosions mentioned have occurred 
during this period, and in cases where life was not involved it is 
quite possible that the occurrence was not recorded. It was also 
found at the beginning of the work, when an effort was being 
made to obtain a record of explosions of this nature, that very 
little definite information was available. Owing to the field being 
somewhat new, data of any assistance was very limited, and 
information pertaining to each explosion was necessarily obtained 
from men who had little knowledge of other accidents of this 
nature. It is possible that explosions of this kind have occurred 
in diflferent sections of the country, reports of which have not 
been published. However, the fact that so large a number of 
occurrences of this kind have taken place during the past year 
is of sufficient importance to attract our attention and demand 
careful consideration. 

Reports show that the same situation exists in European 
countries, especially in milling plants in England.* 

Four of these explosions have occurred in England during 
the last three years, the one at Liverpool, November 24, 1911, 
being exceptionally destructive. A careful study of occurrences 
of this nature abroad would, no doubt, show that dust explosions 
are frequent also in European milling plants. 



♦See reports on the explosion at the works of William Primrose & Co., Ltd., 
by W. S. Smith, H. M. Inspector for Dangerous Trades, 1911. 

Report on explosion at works of J. Bixby & Sons, Formby street, Liverpool, 
by John Jackson, H. M. Inspector of Factories, 1911. 

Report on Explosion at works of Messrs J. Laing, Son & Co., Holt Town, 
Manchester, by John Jackson, H. M. Superintending Inspector of Factories, 1913. 



The Origin and Distribution of Dusts 21 

ORIGIN AND DISTRIBUTION OF DUSTS 

*T IS just as impossible to prevent dust from being 

J\\J produced in the milling industry as it would be to pre- 
\\ vent dust from forming during the mining of coal. 
The milling dusts are usually fine, and owing to the 
necessary absence of moisture are very dry, presenting dangerous 
conditions when in suspension in the atmosphere. There are so 
many different kinds of dust produced in the handling and milling 
of grain that it would be impossible to enumerate them fully in 
this preliminary report. 

Samples of the following dusts have been collected, and the 
conditions under which they have been produced have been 
studied : 

(1) Dusts produced during the process of elevating and 
handling grain, and known as elevator dusts ; 

(2) Wheat flour dusts from rolls, bolters, purifiers, con- 
veyors, packing machines, etc. 

(3) Wheat flour dusts from beams, rafters, elevator 
heads, etc. 

(4) Dusts produced during the cleaning of oats; 

(5) Dust from grinding white corn; 

(6) Dust from grinding yellow corn; 

(7) Dust from grinding oat hulls; 

(8) Oatmeal dust from packing machines; 

(9) Floor dusts from elevator sweeping; 
(10) Oat groat dusts after aspirator. 

A total of about 150 samples of the various dusts mentioned 
have been collected during the various stages of elevating and 
grinding. 

Elevating Process 

During the process of elevating grain from the boats or 
railroad cars large quantities of dust are produced. The coarse 
or heavier dust settles on the floors, steps, machinery, etc., while 
the very fine dust rises into the atmosphere, and settles on beams, 
rafters and other inaccessible points. The usual system adopted 
for the removal of this dust is by the ordinary "push broom" 
method, and although at the time the very coarse and heavier 
portions of the dust is removed, the finer or more dangerous 
portion rises into the atmosphere and settles along with the other 
fine dust already accumulated from the elevating process. 



22 The Explosibility of Grain Dusts 

Escape from Machines and Conveyors 

The bolters, rolls, purifiers, etc., all produce a large quantity 
of dust during their process of operation, and if a satisfactory 
system of dust collecting is not installed a portion of the dust 
may escape into the surrounding atmosphere. During the grind- 
ing process of any of the grains, considerable dust is produced 
that may also escape into the air if proper provisions are not 
taken to keep the machinery in repair. The conveyor lines and 
elevator legs also carry continually a very large quantity of fine 
dust, and in case of any defect in construction will allow the dust 
to enter the surrounding air. At the discharging point of grain 
into storage, an opportunity is given for the dust to escape into 
the air and settle on surrounding projections. In addition to the 
various sources enumerated, there are possibly a number of 
others, but the ones mentioned generally cover the sources that 
produce the largest quantity. An important consideration in the 
prevention of the accumulation of dangerous dusts would be to 
attack the point where the dust is produced, and not deal exclu- 
sively with its removal after it has settled in dangerous 
quantities. It is true that the entire escape of dust cannot be 
prevented, but it can be reduced to such an extent that its com- 
plete removal can be more certain. 

Oat Hull Grinding 

One of the lines of milling that seems to be accompanied by 
a large number of explosions is the grinding of by-product mate- 
rial, especially oat hulls, in the production of feeds. It is not by 
any means to be concluded that this is the only source of danger, 
but our attention has been drawn to the large number of occur- 
rences of this nature in more recent years. The oat hulls are 
ground by various types of attrition mills, and as a rule the plates 
are set very close together for fine grinding. 



EFFICIENCY OF DUST-COLLECTING SYSTEMS 

I HE INTRODUCTION of dust-collecting systems in the 
77i lit milling industry has succeeded in the practical elim- 
^i' (Is ination of the old dust or "stive" room. When this 
dust room was in use, such as at the time of the 
Minnesota explosion in 1878, and the Illinois explosion in 1893, 



Efficiency of Dust-Collecting Systems 23 

the dust was conveyed or carried to the "stive" room from the 
various parts of the mill. This always made an "explosive 
chamber," as it were, allowing sufficient dust to be in suspension 
to produce a violent explosion, if ignited. With the present 
system of dust collection as applied to modern mills this particular 
source of danger is done away with, and, by means of air cur- 
rents, the dust is carried to the collector and deposited. Many 
millers seem to feel a sense of security if such a dust-collecting 
system is in good working order, and that this danger from explo- 
sions is practically eliminated. Owing to the difference in types 
of grinding machines used in flour and feed milling, the flour 
miller feels an additional amount of protection from the fact that 
a series of sparks necessary to ignite the dust cloud, will not be as 
readily produced by the grinding "rolls" as when attrition or 
friction mills are used. However, it would not be advisable to 
conclude that flour mills are not as liable to experience explosions 
as feed or cereal mills, owing to this one difference of machinery 
installation. In addition to the mill proper, fires very frequently 
occur in the elevator buildings. Since experiments have shown 
that the elevator dusts are highly inflammable, it is possible to 
initiate a violent explosion in the elevator annex that may spread 
throughout the entire milling plant. The relation between the 
elevator and the mill buildings is so close at many milling plants, 
that an ignition of dust in one may readily propagate to a violent 
explosion in the other. 

During the progress of the study now being conducted the 
efficiency of the different types of dust-collecting devices received 
considerable attention. With the advances in milling many com- 
panies utilized the by-products from the grains for feeds, which 
necessitates, in many cases, very fine grinding, thereby producing 
a very large amount of dust. The efficiency of the various types 
of dust collectors installed to collect the dust produced, introduces 
an important point for consideration. 

Observations in various mills would seem to indicate that at 
times some of the dust collectors do not work as effectively as 
at other times. In some cases dust has been in suspension, 
forming a noticeable cloud near the collecting device, probably 
due to defective equipment. When this occurs the very finest 
part of the dust leaks out into the atmosphere, and when mixed 
with sufficient air forms a dangerous mixture. 



24 The Explosibility of Grain Dusts 

Relation of Dust-Collecting Systems to Explosions 

The relation that the dust-collecting system has to the pro- 
pagation or spreading of the explosion is of sufficient interest to 
demand attention. This would appear especially true when we 
observe that many explosions have occurred in recent years where 
dust-collecting systems were said to have been installed and in 
operation throughout the plant at the time of the occurrence. 
The question arises as to how efficiently these systems were 
operating at the time of the explosion. The fact that it is 
possible to have disastrous explosions in plants that are 
considered modern, as far as provision for dust collecting is 
concerned, would give sufficient reason for an investigation to 
determine the relation between the efficiency of the system and 
the propagation of the explosion. 

Some types of dust collectors are constructed in such a 
manner that it requires a series of "air draft lines" to complete 
the system. The circulation of air produced by the fan allows 
sufficient air current in circulation to keep a possibly dangerous 
amount of dust in suspension within the enclosed area, whether 
it be a pipe, box or conveyor line. This dust cloud, when ignited, 
will readily propagate to a disastrous explosion. 



LABORATORY INVESTIGATIONS 

Introduction 

>HERE are a great many questions and problems in a 
/|T V§ grain dust investigation for both the engineer and 
w ^ chemist. Among the latter are to be considered the 
V^==:si^=;^ chemical nature and composition of the dusts, their 
ignition-temperature and explosibility, — as they occur, and also 
of the fine material contained in them, — the effect of humidity, 
moisture and chemical composition upon their explosibility, and 
also the effects of oxidation. The present laboratory study of 
these dusts was undertaken to determine some of these factors, 
and others that may suggest themselves, such as sources of 
possible ignition. 

The results given herein are preliminary, and are given 
simply as an indication of what is being done and what may be 
expected in future work. They should not be considered as 
absolute, but as giving a possible comparison of the chemical 



Laboratory Investigations 25 

composition, and also of the explosibility of the dusts tested. Any 
suppositions or possible conclusions that may be drawn are 
subject to change as the result of future work. 

Previous Work 

A large amount of work has been done upon the inflamma- 
bility of coal dusts abroad and in the United States, but very little 
in comparison has been done upon other carbonaceous dusts such 
as those produced in milling industries. In 1845 Faraday and 
Lyell gave out the supposition that coal dust in suspension in air 
might propagate an explosion started by firedamp. This is doubt- 
less the first suggestion made that coal dust would propagate a 
flame. For many years it was overlooked. In 1873 Watson Smith 
published in the Glasgow Herald the fact that a mixture of dry 
flour and air was inflammable. 

Following the diseaster in Minnesota in 1878, Professors 
Peck and Peckham* carried out some tests upon the explosibility 
of flour dusts. They found that two ounces of these dusts 
together with two cubic feet of air would produce, when ignited 
in a box with a flame, an explosion that would lift two men 
standing on the cover. It has been calculated' that a sack of flour 
suspended as dust in 4,000 cubic feet of air (a room 20x20x10) , 
when ignited, would generate sufficient force to throw 2,500 tons 
100 feet high. 

More recent work upon the inflammability of carbonaceous 
dusts other than coal has been carried out by R. V. Wheeler, 
Chief Chemist for the Explosion in Mines Committee, England.* 
He tested a large number of various kinds of dusts by two 
different methods — one for the purpose of discriminating between 
harmless and dangerous dusts; the other with the intention of 
ascertaining the temperatures at which inflammation of the 
dangerous dusts takes place readily. As a result of these tests 
he divided the dusts into three classes, namely: — 

"Class 1. — Dusts which ignite and propagate flame readily, the source 
of heat required for ignition being comparatively small; such, for example, 
as a lighted match. 



*Mines and Minerals, 1908, 29, 55. 

tC. E. Munroe, J. Amer. Chem. Soc, 21, 321. 

JReport on the Inflammability and Capacity for Transmitting Explosions 
of Carbonaceous Dust, Liable to Be Generated on Premises, Under the Factory 
and Workshop Acts. 1913. R. V. Wheeler, D. Sc. 



26 



The Explosibility of Grain Dusts 



"Class II. — Dusts which are readily ignited, but which for the propaga- 
tion of flame require a source of heat of large size and high temperature 
(such as electric arc), or of long duration (such as the flame of a Bunsen 
burner). 

"Class III. — Dusts which do not appear to be capable of propagating 
flame under any conditions likely to obtain in a factory; either (a) because 
they do not readily form a cloud in air, or (l>) because they are contaminated 
with a large quantity of incombustible matter, or (c) because the material 
of which they are composed does not burn rapidly enough." 

Dusts of interest in the present investigation were classified 
by Wheeler as follows: 



Class I: Sugar 
Starch 

Rice, meal and sugar refuse 
Wood flour 
Malt 
Oat husk 

Class II: Rice milling 

Castor oil meal 
Off^al grinding (bran) 

Class III: Spice milling 
Cotton seed 
Cotton seed and soya bean 



Grain (flour mill) 
Maize 

Grain (grain storage) 
Rape seed 
Cornflour 
Flour (flour mill) 

Grist milling 
Horn meal 
Mustard 

Sack cleaning 

Rape seed (Russian) 

Grain cleaning 



The classification, as here given, is according to the inflamma- 
bility of the sample tested. Other results might be obtained 
from other samples of the same material, especially those placed 
in Class III. 

In the first test which he used he determined the relative 
ignition-temperatures of the dusts, that is, the temperature to 
which the dust must be heated before it will propagate a flame. 
For this purpose he used a glass cylinder (Fig. 1) 8 cm. (3.14 
inches) in diameter and 140 cm. (55.14 inches) long, open at both 
ends, and supported in a horizontal position. A platinum coil of 
32-gauge wire, closely wound on a thin-walled tube of quartz of 
capillary bore, passed horizontally across a cylinder at a point 
40 cm. (15.75 inches) from one end. Through the bore of the 
quartz tube a platinum vs. platinum-rhodium thermo-couple 
passed, and was connected to a mille-voltmeter calibrated so as to 
read temperatures on the Centigrade scale. By means of suitable 
connections an electric current could be passed through the plat- 



Laboratory Investigations 



27 



inum coil so that it could be heated to any temperature up to 
about 1400° C. (2552° F.), and maintained at a constant tem- 
perature by the adjustment of the external resistance. The length 
of the heated coil was 17 mm. (.669 inches) and its diameter was 
1.5 mm. (.059 inches). 






A 






Z)us^ So be lesieeZ 



Plaivrt t4,m. colZ 




^ea^ejTO cu^re?t,t 









£rt.lajn^e<i scc^coft. ojcj'os.f c.d. 



Two grams (.07 ounces) of the dust to be tested was placed 
in an even layer along a glass tube of 2.5 cm. (0.97 inches) 
internal diameter, 45 cm. (17.8 inches) long. This tube was 
closed at one end by a rubber stopper carrying a glass tap of 

I cm. (.39 inches) bore. It was supported in the position shown 
in the diagram (Fig. 1), the open end being at a distance of 30 
cm. (11.8 inches) from the heated platinum coil. The tap was 
connected with an arrangement for giving a constant puff of air, 
consisting of a brass cylinder 65 cm. (25.85 inches) long and of 

II cm. (4.35 inches) internal diameter, fitted with a piston 
weighted so as to give a pressure of 2 pounds per square inch. 

The platinum coil having been heated to such a temperature 
as preliminary trials may have indicated as being about that 
required, the dust cloud was produced by suddenly opening tap B. 
The air blast, passing over the surface of the dust in the tube 
(A), raised the top layer and carried it into the larger tube and 
over the heated coil in a cloud that remained uniform during the 



28 



The Explosibility of Grain Dusts 



stroke of the piston. If ignition occurred the temperature of the 
platinum coil was lowered 10-20° C. (18-36° F.) and a fresh trial 
made; and so on until two temperatures were obtained differing 
by 10° C, at one of which inflammation took place, whilst at the 
other the dust cloud passed over uninflammed. The mean tem- 
perature was thus taken to be the ignition temperature of the 
dust under the conditions of the test. 

Using this method on the dusts listed above (all of which 
were dried during one hour at 107° C), Wheeler gives the follow- 
ing results, which show the relative ignition temperature of 
the dusts: 



Percentage 
of sample as 

received Igni- 
that passed tion 
a 200-mesh Tern. 
Substance. sieve. Degr. C. 

Wood flour Fluffy, 

could not 
sieve 
Rice meal and sugar 

refuse Fluffy, 

could not 
sieve 

Rape seed Did not 

sieve, 

sample 

too small 

Rape seed (Russian) 90 

Castor oil meal 50 

Grain (flour mill) 50 

Spice milling 50 

Grist milling 30 

Sack cleaning Fluffy, 

could not 

sieve 

Rice milling 20 

Offal grinding (bran).. 75 980 

Sugar 50 805 

Grain (grain storage)... 20 1050 

Starch 80 1035 



Remarks. 



985 Cloud formed easily, although 
the sample was unsieved. 



970 Cloud formed easily and flame 
traveled rapidly in it. 

1050 Ignition temperature probably 
lower, but no more dust 
available. 

No ignition. 

1100 
995 

A small flare appeared at the 

coil at 1000° and upward, 
but no flame was propagated. 

A small flare at coil, but there 

was no propagation of flame. 

No ignition. 

Small flare at coil, but no pro- 
pagation. 



Flame traveled very rapidly in 
the cloud. 



Laboratory Investigations 



29 



Percentage 
of sample as 

received Igni- 
that passed tion 
a '200-mesh Tem. 
Substance sieve Deg. C Remarks 

Starch 100 960 Flame propagated rapidly. 

Grain cleaning No ignition. Sample much too 

coarse to form cloud. 

Horn meal 50 No ignition, a few sparks only. 

Oat husks 90 990 

Malt 50 990 Flame propagated rapidly. 

Mustard 50 1050 

Flour 90 1060 

Maize 70 1010 

Cornflour 90 1060 

The second test carried out by Wheeler, to determine the 
lowest temperature at which ignition can be effected, consisted 
in passing the dust cloud down through a tube heated by means 
of a copper coil. As a result of these tests he gives the following 
data: 

Ignition "Percentage of in- 

teniperature combustible 

Substance. Deg. C. matter. 

Wood flour 610 3.2 

Rice meal and sugar refuse 630 8.1 

Rape seed 650 No dust for analysis 

Castor oil seed 655 23.1 

Grain (flour mill) 630 18.2 

Spice milling 680 

Very small flare 29.9 

Grist milling 600 7.8 

Sack cleaning No ignition could 

be obtained 74.6 

Rice milling 630 4.2 

Offal grinding (bran) 640 30.0 

Sugar 540 1.4 

Grain (grain storage) 630 10.5 

Starch 640 1.5 

Starch 630 0.4 

Grain cleaning Dust not tested; 

much too coarse 8.9 

Horn meal 670 5.3 

Oat husk 620 13.4 

Malt 600 11.7 

Mustard 680 5.1 

Flour 650 1.5 

Maize 645 8.0 

Cornflour 620 0.9 



30 The Explosibility of Grain Dusts 



Outside of the work referred to, very little published work 
of importance has been done upon carbonaceous dusts other than 
coal dusts. 

Experimental Work 

The original laboratory work in this investigation was started 
in the United States Food and Drug Laboratory, Chicago, under 
the direction of Dr. A. L. Winton. Twenty-one samples of repre- 
sentative dusts were analyzed, using the methods in vogue in 
that laboratory. Determinations of moisture, ether extract, 
proteins, crude fiber, ash, and nitrogen free extract or carbo- 
hydrates, were made to determine, not only the chemical nature 
of the materials, but also wherein they might differ from the 
grains from which they originated. These results will be given 
in a table below. 

At the completion of this part of the work, direct experi- 
ments upon the explosibility of these dusts were begun in the 
Bureau of Mines laboratories, Pittsburgh, under the direction of 
Dr. J. K. Clement. The first tests carried out were with the 
French apparatus, as used by M. J. Taffanel. This consisted of a 
tube in which was placed 0.5 gram (.0176 oz.) of the dust to be 
tested. This was connected with a canvas bag, inflated with 
oxygen under 400 cm. (15.7 in.) of water pressure. The tube 
carried a stopcock which, when opened, allowed the dust to be 
forced by the oxygen, in a cloud, upon a benzine lamp gas flame. 
A relative inflammability of the dusts could be obtained by noting 
the nature of the flame, and the intensity of the report, if any 
resulted. Definite results could be obtained only photographically, 
but this has been postponed to a later date. All the dusts tested, 
which were the same as those analyzed, were found to be inflam- 
mable, even when using air in place of oxygen to force the dust 
cloud upon the flame. 

Ignition-Temperature 

Experiments were then started to determine the relative 
inflammability of the dusts, using the method of Wheeler, out- 
lined above in his first tests. The apparatus as used in these tests 
was a modification of that used by Wheeler. Instead of a long 
glass tube carrying a platinum coil 15.75 inches from one end, 
two tubes of 3 inches internal diameter were used, these fitting 
into a cast iron, asbestos-lined collar, which carried a coil of 
32-gauge platinum wire, simflar to that used by Wheeler, but 



Laboratory Investigations 31 



1 inch long, 14 inch external diameter, and covered with a thin 
coating of alundum cement to protect the wire. The tube holding 
the dust was % inch diameter and 6i/i inches long, slightly con- 
stricted so as to make the dust cloud carry further. It was 
placed in the larger tube, near the top, with its constricted end 
12 inches from the coil, and the tube inclined so that the inner end 
was 14 inch higher than the outer end. This was found advisable 
to obtain a uniform dust cloud, filling the large tube at the point 
where the coil was inserted. In place of the piston used by 
Wheeler a 5-liter bottle, fitted with a mercury manometer, and 
inlet and outlet tubes, was used. This was filled in each test with 
air under 2 pounds pressure. 

In determining the ignition-temperature, tests were carried 
out until temperatures were reached where ignition was obtained 
at least twice at one temperature, and not obtained twice at a 
temperature 10° C. (18° F.) lower. It was noted with many 
dusts that flames of different lengths could be obtained consist- 
ently at temperatures varying but slightly from those where tlie 
flame was propagated the entire length of the tube. For instance, 
with Pittsburgh standard coal dust, the following results were 
obtained: 

Temp. Deg. C. Nature of Flame. 

1193 Long; out of tube 

1190 Two-thirds length of tube 

1180 About 4 inches long 

1175 About 2 inches long 

1180 About 4 inches long 

1170 About 2 inches long 

1160 About 1.5 inches long 

The ignition-temperature in tests of this kind was taken to 
be the mean of the temperatures where the flame was propagated 
over half the length of the tube, and the temperature where it 
was short; in this case taken as 1185° C. 

As the resistance of the platinum coil changes with use, and 
the coating upon the coil was not constant, due to disintegration 
or to the deposition of ash upon it, the tests were run against a 
standard, and the results referred to it in each case. Since no 
standard has been established for carbonaceous dusts, other than 
coal dust, and since a large amount of work done by the Bureau 
of Mines has shown that Pittsburgh Coal Dust is very uniform 



32 



The Explosibility of Grain Dusts 



and that its changes are practically negligible, and since a large 
quantity of it was available, it was taken as a standard. After 
determining the ignition temperature of each dust, that of the 
standard was obtained and the results given referred to the 
standard value. This value was arbitrarily taken as 1185° C. 
(2165° F.), since it was the value usually obtained when the coil 
was in the best condition. If the ignition-temperature of a certain 
dust was found to be 1005° C, and that of the standard of the 
same day was 1175° C, by referring these values to the standard 
temperature for the coal dust (1185° C.) the ignition-temperature 
of the dust tested would become 1015° C. (1859° F.). This is 
done also to make the results more comparable. Since this is 
arbitrary, and since the temperatures are the mean of two tem- 
peratures, 10° apart, the results are given only to the nearest 
5° Centigrade. 

In each test three minutes were taken to raise the coil to the 
desired temperature, and then it was held there for two minutes, 
so that the conditions would be uniform and consistent in each 
test. 

The results of the analytical work, as well as the tests to 
determine the relative ignition-temperature, are given here so 
that any comparisons that may be desired can be easily drawn : 



Table I 



6 


Kind of Dust. 


Condition. 


6 

3 

o 


m 




Protein 
from N. 
Factor 6.25 


m 



6 
o 


Ignition 
Temp. 


'A 


4) 

u 




13 


Wheat — Ele- 


As received- 
Sieved 100m 
As received- 
Sieved 100m 
Sieved 80m.. 

As received. 
Sieved 100m 


7.15 

8.063 

7.13 

5.82 

5.63 

6.89 
8 23 


3.15 

2.938 

5.16 

4.60 

5.32 

2.71 
2 50 


16.63 
11.86 
16.79 
9.17 
11.61 

18.56 
14.805 


13.38 

15.125 

13.19 

13.25 

13.38 

11.31 
12.97 


1 
15.97 43.72 
16.775 45.239 


129512363 
1 


15 


Wheat — Ele- 
vator, marine 


15.04 
16.43 
16.465 

11.93 
14.905 


42.69 
49.76 
47.595 

48.60 
46.59 


Too lumpy, 
not form 
cloud 


17 


Wheat — Bet. 
elev. and stor- 


1295 


2363 


23 


Flour — Dust 




















from top of 
elev. head 


As received.. 


9.565 


1.80 


0.515 


13.065 


0.755 


74.30 


1235 


2255 


25 


Flour — Dust 
from purifiers 


As received. 


9.00 


3.51 


2.83 


12.16 


1.71 


70.79 


Too 


moist 


33 


Flour — Fin. 
















and lumpy 




product from 
pkg. room 


As received. 


9.57 


1.38 


0.20 


12.51 


0.56 


75.78 


1265 2300 



Laboratory Investigations 



33 



% Kind of Dust. 


Condition. 


u 

3 
m 

o 


Fats. 


.a 

« 

■a 

3 
u 
U 


01 g o 
lit 


o 


Ignition 
Temp. 


05 


Starch 
Diffe 


U 


1 


35, Wheat — Dust 


As received. 


7.87 " 


2.655 14.675|16.22 


16.21 42.37 


1200 


2192 


from sidewall 


Sieved 200m 










1115 


2039* 


and elevator.... 
















37, Oats and corn 


As received.. 


8.37 


2.43 


7.27 8.66 


13.26 


60.01 


1000 


1832 


— D u s t from 


Sieved 100m. 


8.29 


2.463 


2.30 8.44 


14.765 


63.74 


995 


1821t 


unloading sta. 


















43, Oats and corn 


















— D u s t from 


As received. 


8.29 


2.30 


4.11 7.78 


12.84 


64.68 


995 


1821 


top of elev 




7.38 






10.22 


13.82 




1015 


1859 


47, Oat s — Dust 


As received. 


7.67 


4.80 


6.48 


10.16 


14.70 


56.19 


1010 


1850t 


from feed oats 


Sieved 100m 


















49, White corn — 














" 




Dust from 


As received- 


8.87 


7.73 


1.53 


10.28 


2.09 


69.50 


Too moist 


drier room 

53, White corn — 














and lumpy 


Drying of 


As received. 


7.46 


9.53 


1.92 11.43 


2.59 67.09 


Too moist 


germ 


As received- 


6.65 


5.285 




4.86 61.225 


and }n>^T'»'v 


57, O at s — Dust 


8.82 


13.16 


1020 


1868 


from ground 


Sieved loom 


7.23 


5.665 


3.90 


14.63 


4.445 64.13 






oat hulls 










61, Yellow corn — 




















First break in 


As received.. 


10.06 


0.17 


0.28 


2.595 


0.475 


86.42 


1025 


1877 


dry milling 




















63, Yellow cor n As received- 


8.71 


2.87 


1.50 


6.54 


1.15 


79.23 


Too inoist 


dust 

65, Feed — Dust As received.. 


8.40 
8.925 


1.335 


7.01 

1.19 7.54 


9.00 
9.96 




and lumpy 
Too coarse 


from dust col- 


Sieved lOOm 


71.05 


1015 1859§ 


lector 
















67, Yellow corn — 


















Dust from 


As received.. 


8.72 


4.125 


1.525 


7.065 


1.275 


77.29 


Too moist 


drier 


As received.. 


7.50 


9.215 


0.61 


15.065 


1.78 


65.83 


and lumpy 
Too coarse 


81, Oat groat dust 


















granular 


89, Oats — Ground 
oat hulls from 


Very coarse 
As received.. 


6.79 


5.39 




14.22 


4.28 




1280 2336 


attrition mill.. 


Sieved lOOm 


7.43 


4.82 


0.42 


13.78 


3.13 


70.42 


Not 


97, Reduction mid- 
















enough 


dliiiiirs 


As received.. 


9.15 


1.12 


0.21 i 12.75 


0.47 


76.30 


1280|2336 


103, Flour — Dust 




















from rolls and 




















purifiers b e - 




















fore reel 


As received.. 


8.40 


1.36 


0.71 


14.12 


0.75 


74.66 


1270 


2318 







Sieved through 200-mesh screen — *S0%, t81.2%, {81%, §57% of total. 



It should be noted that these results are only relative, but 
still they can be considered as showing a relation between the 
inflammability of these different dusts. The results thus far 
obtained in these tests seem to indicate that the oat and yellow 



34 The Explosibility of Grain Dusts 

corn dusts are the most inflammable ; the fine material in the side 
wall wheat elevator dust being the only other that has an ignition 
temperature even approaching those for oat and yellom corn 
dust. Sufficient work has not been done upon white corn dust to 
warrant any statement, but present indications are that it is not 
as inflammable as either oat or yellow corn dusts. More complete 
data, to be obtained in future work, may change these present 
assumptions, so they are given only as an indication of what may 
be expected. 

In order to give some idea of the way these tests are carried 
out, as well as to show how an inflammation caused by such a 
small source of heat may be propagated, a few photographs of 
inflammations produced in the English apparatus are given here. 

The point of ignition is within the collar, which shows dark 
in the photographs. The tube which holds the dust is also shown 
at the extreme right end of the pictures. The dust is blown from 
this tube against the heated coil, where it is ignited. It is shown 
here very conclusively that the inflammation is propagated in 
both directions from the point of ignition, but that the largest 
flame travels in the direction in which the dust cloud is originally 
forced. 

A distinct difference will be noted between the inflammation 
of the oat hull and yellow corn dusts. The flame of the former 
is the longer, while that of the latter is more bushy outside the 
tube. This may be due to the fact that the former was the 
coarser, and consequently burned for a longer period. Very 
strong detonation accompanied the ignition of the corn dust, loud 
enough to attract the attention of persons working in the same 
building, but at least 100 feet away. The ignition of the former 
was accompanied by a very slight detonation. 

The two photographs of ignitions of oat and corn dust from 
unloading station show very well the difference in the propagation 
of flame at temperatures varying by only 20° C. (36° F.). 

It has been thought by some milling men that certain dusts 
were not dangerous. These photographs show beyond all ques- 
tion that these dusts will ignite and propagate a flame under the 
conditions of the experiment. By similar photographs it could be 
shown that all the dusts thus far considered will propagate a 
flame under proper conditions. The work that was first carried 
out with the French apparatus also confirms this statement. 



Laboratory Investigations 



35 




No. 37. Oats and Corn: Dust from Unloading Station, 

Sieved 200-mesh screen 

Temperature 1170° C, '2138°F. 




No. 37. Oats and Corn : Dust from Unloading Station, 

Sieved 200-mesh screen 

Temperature 1150° C, 2102° F. 



5373 

No. 37. Oats and Corn: Dust from Unloadinj); Station, as received. 
Temperature 1200° C, 2192° F. 



36 



The Explosibility of Grain Dusts 




No. 57. Oats : Dust from (jround Oat hulls as received 
Temperature ll.)0° C, 210^2° F. 




No. 61. Yellow Corn: Dust from first break in Dry Millino;, as received 
Temperature 1150° C, 2102° F. 



Laboratory Investigations 37 

Relative Inflammability 

Considerable work has been carried out in the Bureau of 
Mines in perfecting a laboratory method for determining the rela- 
tive inflammability of coal dusts. Dr. J. C. W. Frazer worked 
upon a method for the determination of the pressure created 
when the various dusts are ignited at a fixed temperature. A 
description of the same is given in Bulletin 50 of the Bureau of 
Mines. This apparatus has been modified by Dr. J. K. Clement, 
and his associates in the Bureau of Mines. As used at present it 
consists of an explosion flask of about 1400 c.c. (85.36 cu. in.) 
capacity, a platinum coil, a device for driving a dust cloud against 
the coil, and a Crosby pressure-gauge, for measuring the pressure 
developed. The flask is provided with tubulures at its top and 
bottom, the ends of which are ground true. The smaller tubulure 
rests on a circular brass plate, carrying a small brass funnel con- 
nected into it. A circular brass plate rests on the top of the 
tubulure and carries the platinum coil, holding it near the center 
of the flask by means of steel leads, passing through bakolite 
stoppers. This plate also carries a brass tube, which is connected 
to the Crosby gauge. The contacts between the tubulures and 
the brass plates are made tight by rubber washers. The lower 
plate rests in a groove in a wooden block, carrying two upright 
rods, having a thread and nut on the upper ends. A long steel 
plate, cut in at each end and cut out in the center to allow the 
leads and brass tube of the upper circular brass plate to pass 
through, rests upon the upper plate and extends over the upright 
rods. By screwing the nuts down upon this plate the entire 
apparatus is made gas-tight. The platinum coil is wound on a 
hardened lavite tube one inch long, grooved, and of capillary bore. 
The coil is covered with a coating of alundun cement. Through 
its capillary passes a platinum vs. platinum-rhodium thermo- 
couple, which is connected to a mille-volt meter, graduated to 
read degrees Centigrade. The leads holding the coil are con- 
nected to the terminals of a storage battery through a lamp 
back, rheostats, and an ammeter, by which the amount of cur- 
rent can be regulated and determined. 

For each determination 50 m. g. (.00176 oz.) of the dust is 
weighed into the glass funnel and shaken down as far as possible 
into the bend in the stem of the funnel, which is connected by 
rubber tubes to a check valve, and thence to a 150 c. c. glass bulb 



38 The Explosibility of Grain Dusts 

used for an air reservoir. This is connected to a mercury mano- 
meter, and then to a source of compressed air. Air is forced into 
the small reservoir until it is under a pressure of 190 m. m. of 
mercury (4.75 lbs.). 

After weighing the sample into the funnel the flask is placed 
over it, the coil, brass plate and gauge placed in and on the flask, 
and the whole fastened tight, except for a small opening in the 
brass tube. The current is turned on and the desired temperature 
gradually reached in three minutes, and then held there for two 
minutes to obtain uniform conditions in the flask. At the end of 
the five minutes the small opening in the brass tube is closed, and 
a pinch-cock between the check valve and the air reservoir is 
opened and the dust thus forced in a cloud against the coil. The 
pressure developed is recorded by the gauge pointer upon a 
smoked drum and can be measured whenever convenient. 

As was the case in determining the relative ignition-tem- 
perature, no standard has been determined for carbonaceous 
dusts other than coal dust, consequently to obviate changes in the 
coil, and for other reasons given above, each sample was run 
against Pittsburgh Standard Coal Dust, and all values referred 
to it as standard. In running these tests a determination was 
made upon the standard alternately with determinations upon the 
dust being tested. These results were then averaged, and the 
values which were obtained referred to the standard pressure for 
the coal dust, which was taken as the average of the results 
obtained each day during the tests. This value for 1200° C. was 
9.0 pounds, for 1100° C. was 7.0 pounds, and for 1000° C. was 0.5 
pounds. The value given below for 900° C. (0.1 pound) is that 
obtained in previous work done in the Bureau of Mines. In 
referring the results obtained on the cereal dusts to the standard 
values for Pittsburgh Standard Coal dust the following proportion 
was used : 

Average pressure for cereal dust : Average pressure obtained 
in test upon standard : : x : standard value for coal dust at 
temperature of the tests. The value obtained for x is then com- 
parable to the values obtained for every other dust, irrespective 
of changes in the coil. 

A certain pressure is always developed within the flask by 
the inrush of the compressed air, but this is small, 0.3 to 0.4 of a 
pound, and was corrected for in each case. As indicated in the 



Laboratory Investigations 39 



following tables and curves, tests were made upon samples as 
received, upon that portion of some samples which passed a 200- 
mesh sieve, and also upon samples dried at 105° C. for three hours 
in a current of dry air. 

Since in most cases the dusts as received contained consid- 
erable and variable amounts of coarse material, the results 
obtained upon these should not be compared. For the same reason 
it was very difficult to obtain consistent results, for it was not 
possible to obtain a uniform sample when such a small amount 
was used. Therefore in the subjoined table a column of high 
results is given, which indicates what may be expected under 
certain conditions. 

Before considering the results of these tests it shall be noted 
that the temperatures which are given are the temperatures on 
the inside of the coil, and not at the point of ignition. The tem- 
peratures on the outside of the coil are necessarily lower on 
account of radiation of heat ; however, this would be constant in 
each test, since the heating interval is always the same, and 
therefore the results are comparable. To obtain data relative to 
the probable temperature on the outside of the coil observations 
were made upon it with an optical pyrometer. The averages of 
several tests gave the following: 

Temperatures inside of coil. Temperatures at surface of coil. 
1200° C. 1075° C. 

1100° C. 990° C. 

1000° C. 915° C. 

While these may not be accurate, due to personal error in 
reading the optical pyrometer, they show that the outside tem- 
peratures are considerably lower than the inside temperatures. 



40 



The Explosibility of Grain Dusts 



Table II 



ji Kind of Dust 



Condition 



Pres. in lbs. 

at 1200° C. 

(2192° F.) 

Referred to 

Pffh. std. dust 

at 9.0 lbs. 



Aver 



Hisrh'st 



2o 

5° 
.2^ 



Pres. in lbs. on dried sam- 
ples ref d to Pgh. std. dust 



1200° C 
21920F 



1100° C 1 1000° C 
2012° PI 1832° F 



900° C 
1652o P 






13, Wheat — Ele- 
vator dust 



As received.. 
Sieved 100m. 
Sieved 200m. 



As received- 
Sieved 200m. 



As received... 
Sieved 200m. 



As received... 
As received... 



As received... 



Sieved 200m.. 



As received... 



As received.. 



6.5 

9.2 



8.5 
9.5 



17, Wheat — Dust 

between top of 

elev. and stor- As received. 

age tanks Sieved 100m. 

23, Flour — Dust 

from top of I 

elev. hds As received 

33, Flour — Fin.l 

product from 

pkg. room [As received 

35, Wheat — Dust 

from sidewall 

of elev 

37, Oats and corn 

— D u s t from 

unloading sta. 
43, Oats and corn 

— Dust top of 

elevator.... 
47, O a t s — Dust 

from feed oatsjsieved 200m. 
49, White corn — 

Dust from 

drier room 

57, O a t s — Dust 

from ground As received. 

oat hulls 

61, Yellow corn — 

Dust from first 

break in dry 

milling 

63, Yellow corn — 

Dust from col- 
lector 

65, Feed — Dust 
from dust col- 
lector Sieved 200m. 

97, Reduction 

middlings As received. 

103, Flour — Dust| 
from rolls andl 
purifiers jAs received. 



5.0 
5.7 



5.8 

7.2 



6.0 7.0 



5.8 



6.8 
9.9 



5.8 



7.2 
11.1 



4.5 6.1 
11.1 I 11.3 



11.1 I 11.7 

6.3 7.6 

12.6 12.8 



0.1 



6.5 I 9.6 
10.3 I 10.7 



15.1 I 16.5 



6.79 



6.31 



8.73 



8.46 



6.57 



7.35 



8.32 



7.36 



12.6 



9.1 



9.1 



7.8 



13.9 



12.8 



7.41 14.6 



6.72 12.2 



11.3 



15.4 



0.5 I • 1 8.77 I 8.3 

I < I 

I I I 

7.9 I 8.7 I 6.44 I 14.3 

0.2 I 'I 8.73 I 8.9 

I I I 

I t I 

0.4 I * [ 8.72 I 8.2 



10.4 



6.9 



11.6 



12.5 



1.0 t 



9.4 



7.5 



8.2 



4.8 



0.3 



10.4 



0.2 



6.8 



0.2 



0.5 



0.1 



4.9 



14.9 



9.5 



9.7 



8.8 



14.2 



14.0 



16.1 



12.8 



13.2 



8.9 



•Too moist and lumpy. tCoarse; would not form cloud. |Not dried. 



Laboratory Investigations 



41 



5 

z 

UJ 

< 

CO 

o 





























1 




























1 












16 








































































No. 47 


Dust from feed oats 


































1 

12.8 

t1 


- 


- 






















1 1 


















\~\ — 


,_ 


_ 


_ 





_ 


_. 


.- 


._ 






















10 


.f 


.- 




~ 


— 


"~ 




































8 


















,'' 


' 




























































^ 


' 






























































^' 


' 


























































-I 




^y 




































































































































































































le 




























































16 










No. 61 Yellow corn, dust from Orst break in dry milling: 
















.1 














































94 








, 


^ 


-- 
























































K- 


■ — 
























8 






































''' 




























































^ 


^ 






























































y 


^' 


























































,5 




^^ 
































































L-^ 


















































































































10 






























































































































89 










No. 97 Reduction middlings 














7.S 








^ 


._ 


- 


-• 


— 






























5.8 
















^. 




t- 




" 












































^ 


- 


-- 


— 






































4. 


U 








.- 


— ' 


-- 


— 


—" 


r 














































6 
























































































































































































































































































































































































































































































































































9 




























































,^ 


-■ 


--■ 














Pittsburgh stand 


ard coal 


dust 
















._ 


— 


— 


" 
























































y 


"' 
































































,x 
































































y 


• 
































































^ 
































































^ 


-' 










































.r 


















* 


/'' 














































_. 


-- 


-■ 


-- 


- 


.... 


— 


-r 













































CENT.900 
FAHR.I652 



1000 
1832 



MOO 
2012 



1200 
2192 



TEMPERATURE —DEG. 



42 



The Explosibility of Grain Dusts 













































































































lb 




No. 13 Wheat elevator dust 






















12 


6 


— 


































10.4 












'■\ 




































-■ 


-- 


~ ' 














8 
















"r- 




-- 


— ' 


" 








































^ 
^ 


^ 
















































^ ' 


^ 












































,0 




^ ' 


" 
















































y 










































































































16 














































































































No. 33 Flour, finished product from packing room 


































































8 






























-6 ^- 














7.8 


















4 


8- 












A 




n 


— 


— 


— 


"" " 


■ ■" 




























• — 


— ' 
































\ 






^ 


,- 


■-•' 












































'"' 










































































































— 


1 
















































IB 


No. 35 Wheat, side wall of elevator 
















1 13.9 




































11.6 






. _ 


-- 


■- 


— 


* "* 






































y' 


" 




















8 




























/" 


^ 
















































• 


















































. 


." 


































1 












T 


y 




















































\^ 


























































































16 
























































1 












































Pittsburgh standard coal dust 












































































( 


) 


— 


8 
































\ 

1 










— - - 


.- 






































<r- 


-- 


*"" 














































• 


























X 














1 




^' 


'" 
































._ 


_ 











__ 


.5 ^ 

-f 


















1 

















CENT. 900 
FAHR. 1652 



1000 noo 

1832 2012 

TEMPERATUr.I- DEC. 



1200 
2192 



Laboratory Investigations 



43 



2! o 

> m 

X z 

30 H 



PRESSURE -POUNDS PER SQUARE INCH 



s g 








10 






4 


Sk 






a> 






o 






o 






to 




A 






a 


S§ 


"^ 


i. 




























































— 


> 






























































N 












I 


















































S 


> 


^ 






















































■0 




\ 


\ 


N 




















































i 




\ 




,^ 


N 


















































a 

c 






V 


% 


s 


s 


s 


s 














































.i. 






\ 


\\'i 




S 


s 






















































\ 


-<v 




\ 


\ 




\ 


















































^< 


k - 




\ 






N 


s 






































,8! 










\ 








s 






\ 






































S 
s. 

a 












C^ 


v 






s 


\ 






\ 












































\ 


i 








\ 


\ 






s 


s 










































V= 


^ 




, 




\ 


s 








N 




























ft 














\ 




k 




S 


s 








N 
























?^ 9 




















V 


> 






S 










S 






















ra o 


^ 


^ 
















\ 


-1 

o 










o 
































^ 


^ 














\ 


kl 


1 


^ 


















,0 
























> 


^" 


s 




% 








\^ 


'• 








u 


• 








>> 
























s 


^ 


\ 


h1 






\ 


i 








\< 








\- 


























\ 


\ 


S 


L'T. 


\ 


\l 








\ 


^ 








\ 


[' 




























\ 


\ 


, > 


n\. 


A \> 








\ 


», 








1 






























\, 


s 


o 
s < 


i> 


s 


\^ 


\^ 










\% 


1 








^ 
































s. 


s 


^i 




^ 








1 


V 








» 






























s 






A 


\ 












\ 


\ 








\"a| 
































\ 






\ 






*/ 


?'* 






\ 


ifr 








\ 




































\ 












nV 


\' 










'w 




































\, 








iS 


Vj 




\ 










1 






































\ 






lv< 


>/. 




\ 










\ 






































V 


\ 




\ 


\ 


ht 


^ 




L e 


fr 






\ 








































\ 


\ 


\ 




s 


s** 


">>. 


Y' 


*'o, 




\ 














M — 




























\ 










K 


\ 


\ 






















Sy 






































\ 






1 
















































\ 


\ 








^ 




\ 


















































\ 


\ 










\ 


\ 


















































1 


1 \ 












M 






y 














































y 














K* 


r. 


\ 














































\ 
















s:-^ 


A 














































\ 
















VM 
















































\ 
















\, 
















































w 
















1 


y 














































^ 


















\.^ 














































\ 
















In 




























































\ 


\ 


% 


























































\ 


\ 




<: 


-> 






































I 


















\ 




\ 


\ 


^' 






































\ 


















\ 




\ 




\ 1 


































1 






\ 












1 




\ 




\ 


























































1 


























































1 1 



44 



The Explosibility of Grain Dusts 



16 






14 
















1 
















a Screened through 200 mesh screen 
















b Screened through 100 mesh screen 


12 


■o 
















10 


'Z 


















~'Z 














i 




c ■? 




o 




















iS a 




c 




















♦- •- 


























a; CI 




M 






















ui bo 




c 






















a a 


























^ t- 









































c 


c 
- o- 














-|-|-f- 


8 






c 


~° 


















•D 

C 






O 
> 


bo 


n 
to 
















•8 


.£ 












c 


c 
















X 






J 






'o 


o 

~ c 


o 

c 


3 
X 


3 


- o 


~o 












of elev 
of elev 
om pai 


e 






~ o 






OJ 




1 


w 


^ 


£ 


3 

E 
o 


E 
2 


o 

■o 
c 

3 

o 


O 

■u 
c 

3 
O 


> 


> 

0) 









'0 

CL 


a 


c 


a 


c 


3 

•D 






§ 





D 


3 


3 


tie 


tic 


o 


o 


3 
■D 


3 

T3 


-D 

E 
- 





1 


1 




a 


4 


T3 


_T3 


_TJ 


_T3 


_T3 

C 
1- 


C 


_E 

o 


_£ 
o 

u 


- > 


~? 


~ O 


~ 


- E 



^ 


^ 


-T3 


2 


C 

o 
o 


E 
o 

3 


E 



t- 

3 

_Q 


o 

C 

-o 


o 

■□ 
c 
« 

-O 


o 

C 

-O 


3 

•a 
-O 


3 

-O 


15 


-1 


> 


> 

-i 


3 
-U. 


3 


— li. 


3 

■D 

1 


3 
n 

X 

5 


"c 

3 



-li. 




h- 


N 


CO 


(~ 


r^ 


r~ 


h- 


lO 


lO 


CO 


CO 


10 


CO 


r~ 


r~ 


CO 




o 


^ 


t 


t 


P3 


CO 


lO 


10 


CO 


CO 






CD 


C4 




~ 


CO 




o 


6 


d 


6 


<5 


d 


6 


6 


6 


6 


6 


6 


6 


6 


6 

z 





6 




z 


z 


Z 


Z 


z 


Z 


z 


z 


Z 


z 


Z 


Z 


Z 


z 


Z 


z 












<o 




"" 




T. 




°= 




ns 




^ 







ORIGINAL SAMPLES AT 1200 C. 
2192" F. 



Laboratory Investigations 



45 



PRESSURE -POUNDS PER SQUARE INCH 



r • 1 ' 

No. 61 Yellow corn, dust from ftfst break in dry; milling- not dried. 



No 43 Oat and corn, dust from t op of elevator 

I I 1 



a No. 66 Feed, dust from dust collector 



a No. 35 Wheat, side wall of elevator 



> m 

X Z 

X -^ 



i; K> 

CD O 

>o o 



a No. 37 Oat and corn dtist from unloading station 



a No. 13 Wheat elevator dust 

\ ^ 

a No. 47 Dust from feed oats 



a No. 57 Oats, dust from ground oat hulls 



b No. 17 Wheat dust between top of elevator and 



No. 23 Flour dust from top of elevator heads 



No. 97 Reduction middlings 



No. 63 Yellow corn dust from dust 



collector 



storage tank 



No. 103 Flour dust from rolls and purifier before reel 



No. 33 Flour, finished product from packing room 



o o 
5 o 



No. 49 White corn dust from drier room 
a No. 47 



a No. 35 



a No. 13 



No. 61 -not dried. 



No. 97 



No. 33 



a No. 47 



a No. 13 



00 o 

u o 

M O 



I 



No. 97 



No. 33 



No. 35 

No. 61 '-not dried. 

No.- 9 7 



No. 33 
No. 13 
No. 47 
Pittsburgh standard coal dust \20O 



Pittsburgh standard coal dust 1 1 OCT 



Pittsburgh standard coal dust 1000 

1 1 i 

Pittsburgh standard coal dust 900^ 



tr to 
CO CO 



s ? 



8 S 



46 The Explosibility of Grain Dusts 



In making comparisons of the results given in the above 
table and curves it should be remembered that they are only rela- 
tive, that they simply indicate the relative inflammability of the 
dusts. Although these values show that certain dusts are highly 
inflammable, igniting at low temperatures, and developing enor- 
mous pressures, it is not possible to state that the dusts which 
produce only 0.1-0.5 pound pressure at 1200° C. are not danger- 
ous. It is very probable that at higher temperatures, which 
might easily be obtained from a naked flame, an electric spark, 
or a flash from a blown-out fuse, or from a motor, these dusts 
might be ignited and propagate a flame with explosive violence. 

These results substantiate in an astonishing way the suppo- 
sition advanced from the determination of the ignition-tempera- 
tures of the dust, namely, that the yeflow corn and oat dusts are 
the more inflammable. This is very plainly indicated in the 
straight line curves of figures V and VI. However, from the 
amount of work that has been done thus far, this supposition 
cannot be stated as a fact, although indications are that this is 
true. It is a fact, though, that the highest pressure, as well as 
the lowest ignition-temperatures that have been obtained in the 
tests made thus far, have been given by oat and yellow corn dusts. 

On the contrary, the results obtained upon the sieved and 
dried samples show that the wheat and elevator dusts are also 
very inflammable, nearly as high pressures being developed by 
these dusts under the condition of the experiments as by the 
oat and corn dusts. If the pressures developed in these tests are 
considered, it will be noted that the two giving the highest pres- 
sures are from oats and corn, the third and fifth are wheat 
elevator dusts, and the fourth is an oat and corn dust. These 
values become more astonishing when we note the percentage of 
ash in the dusts. The oat and corn dusts have from 10 to 15 per 
cent, ash, while the wheat dusts have over 16 per cent. It is not 
possible to state what eflfect a high ash content has upon the 
inflammability of grain dusts, for no work has been done upon 
this ; but from results obtained by the Bureau of Mines upon 
coal dusts it is safe to state that the ash content and its compo- 
sition are large factors affecting the inflammability of these dusts, 
as they are in coal dust. If this is true it is probable that with 
lower ash content these dusts would be much more inflammable, 
but it cannot be assumed that the wheat elevator dusts would 
develop as much pressures as the oat and corn dusts if they had 



Laboratory Investigations 47 

the same percentage of ash. The astonishing fact is that these 
dusts with such high percentage ash will develop such pressures 
under the conditions of the experiments. 

The predominating factor which determines the inflamma- 
bility of a dust has not been determined. Many theories have 
been advanced, such as the amount of volatile matter ; this 
together with the moisture and ash ; the rate or ease of oxidation 
and the degree of fineness of the dust. It is probable that all 
these have an important bearing on the question, and should be 
thoroughly investigated. A discussion of these theories is not 
within the scope of this paper. However, there is one question 
which should be considered, that of moisture. 

It is well known that the humidity of the air has a consid- 
erable effect upon the moisture content of the dusts which are 
exposed to changes in atmospheric conditions. But the effect that 
this has upon the inflammabilty of the dusts is not known. A 
slight indication of what might be expected may be observed in 
comparing the pressures developed in the above tests by the dried 
and undried samples. It will be noted that there was a very 
appreciable increase in pressure deeloped by the dried over the 
undried samples, except in one case — sample 47, dust from feed 
oats. Here a slight decrease is noticed in the average, but this 
may be explained by the fact that fewer tests were made, and 
consequently this is not as fair an average. Especial attention 
should be called to samples 63, 97 and 103. It will be seen that 
the pressures developed by these dusts increased, after drying, 
from 0.5 pound or less to over 8.0 pounds. This can be very 
largely attributed to the difference in moisture content, although 
not entirely, for it is quite probable that if a cloud of the original 
dust, undried, could have been obtained, it would have developed 
considerably more pressure. This raises the question of how 
much moisture would have to be removed from such a dust 
before it could be dispersed in the form of a cloud. The whole 
question of the effect of moisture upon the inflammability of these 
dusts is one which is in great need of thorough investigation. 
Work along this line has been outlined, and will be taken up as 
soon as possible. 

It will be observed that the highest pressure (16.5 pounds 
per square inch) developed by any one dust was developed by 
sample 61, Yellow Corn Dust from the first break in Dry Milling. 
This was obtained upon the undried sample. What pressure would 



48 



The Explosibility of Grain Dusts 



be developed by this dust if it was dried cannot be surmised, but 
it seems likely that it would be considerably higher, for the mois- 
ture content of 10.06 per cent, is higher than that of any other 
dust that has been tested. Determinations upon this sample, 
dried, were not made, because the limit of the apparatus was 
reached with the undried sample. 

To give a better idea of the way the dusts ignite in these 
tests the following photographs of dusts ignited at 1200° C. 
(2192° F.) are given, with the pressures developed in each inflam- 
mation that is shown : 




5379 

No. 33. Flour: Finished Product froniPackin/j Room, Dried. 
Pressure 9.-t pounds 



Laboratory Investigations 



49 




5377 

No. 35. Wheat: Dust from Sidewalls of Elevator, Dried. 
Pressure 11.6 pounds 



50 



The Explosibility of Grain Dusts 




5378 

No. 37. Oats and Corn : Dust from Unloading Station, Dried. 
Pressure I'J.I ])ounds 



Laboratory Investigations 



51 




5380 

No. 57. Oats: Dust from Ground Oat Hulls, Dried. 
Pressure 11.1 pounds 



52 



The Explosibility of Grain Dusts 




5376 

No. 61. Yellow Corn: Dust from First Break in Dry Milling, Undried. 

Pressure 10.1 pounds 



Amount of Dust that will Propagate an Explosion 53 

These show beyond any reasonable doubt that the wheat 
dusts, as well as the others tested, are highly inflammable under 
the conditions of these tests, although they were not as easily 
ignited in the tests made to determine the ignition temperatures 
of the dusts. The pressures developed in these tests are not as 
high in the last four as were developed in the original tests made 
upon these samples, but are not much lower except in the last 
case. This can be explained by the fact that after the test was 
made it was noticed that the valve in the brass tube leading to 
the pressure gauge was not closed. 

Although sufficient work has not been done to allow of any 
absolute statements, the results thus far indicate that all dusts 
that are made in the handling and working up of grain into food 
products can be ignited under proper conditions, and also will 
propagate a flame, most of them with explosive violence. This 
statement should not be taken as meaning that the dusts will 
ignite of themselves, that is, spontaneously ; but when heated to 
their ignition-temperature will ignite and will propagate a flame. 
In other words, there must be some outside source of heat. This 
may be very small, such as a heated coil of wire, as used in the 
above tests, if the temperature is sufficiently high ; or it may be 
larger, as a flame, which may have a lower temperature but a 
larger heating surface. 

If it is true that all these dusts will ignite, as it doubtless is, 
the question of the amount of dust that must be present before 
a flame can be propagated becomes very important. In the tests 
which gave the pressures indicated above, 0.05 gram (.00176 oz.) 
was put in suspension in 1400 c. c. (85.36 cu. in.) of air. To 
obtain the same proportion of dust and air, and therefore a 
mixture as inflammable as was used in the tests, it would be 
necessary to have only 10 pounds of the dust in a closed room 
containing 4,466 cubic feet, or a room 10 x 30 x 15 feet, or 100 
pounds in a room 30 x 15 x 100 feet. This mixture certainly is 
dangerous, and it is very probable that larger amounts of the 
dust in the same space would be more dangerous. This higher 
amount is not as important as a knowledge of the lower limit. 

AMOUNT OF DUST THAT WILL PROPAGATE 
AN EXPLOSION 

Experiments at the Pittsburgh testing station of the Bureau 
of Mines have shown that an explosion could be produced when 



54 The Explosibility of Grain Dusts 

there was only .032 ounce (thirty-two one thousandths — 32/1000) 
of coal dust suspended in each cubic foot of air, or one pound in 
500 cubic feet of air. In order to produce complete combustion 
it takes all of the oxygen in one cubic foot of air to completely 
burn 0.123 ounce (one hundred twenty-three thousandths) of the 
dust used. This dust was sufficiently fine to pass through a 200- 
mesh sieve (one with 200 openings in the length of an inch) and 
floated easily on a strong air current.* From these tests we 
might form a preliminary conclusion, viz., that when the mixture 
contains between .032 and .123 ounces per cubic foot it forms 
an explosive mixture, and one that is extremely dangerous. We 
might term these proportions the lower and higher explosive 
limits of the explosive coal dust mixture. 

In the experiments of M, J. Taffanel at the Lieven experi- 
ment station in France, in one instance as low a weight as .023 
ounce of coal dust per cubic foot of space was sufficient to produce 
an ignition.' At the German station at Derne, an ignition was 
produced when .040 ounce of coal dust was suspended in one 
cubic foot of air.t 

These figures, as given, apply to coal dust tests, and indicate 
that a very small amount of dust in suspension is sufficient to 
produce the original ignition that will propagate to a very disas- 
trous explosion. Preliminary experiments already conducted 
indicate that many of the grain dusts have relatively a lower 
ignition-temperature than many kinds of coal dust ; also upon 
ignition the grain dusts give higher pressures at lower tempera- 
tures than some of the coal dusts. This would seem to indicate 
the possibility of securing an ignition of dust of this nature, 
with a smaller proportion per cubic foot than is necessary for 
coal dust. This, however, has not been definitely determined, and 
will be a matter for future experiment. 

Propagation of Dust Explosions 

The investigations already conducted in connection with pre- 
vious explosions indicate that usually two reports are heard by 
the men who have survived the ordeal and have been able to relate 



*Georg-e S. Rice, Bureau of Mines Circular No. 3 — Coal-Dust Explosions. 

tExplosibility of Coal Dust. George S. Rice et al. U. S. B. M. Bulletin 
No. 20. 

$Colliery Engineer, April 1, 1914, Vol. 24, No. 9. German Coal Dust 
Experiments. 



Measuring Dust in the Air 55 

their experiences. The first report is described as a sharp, quick 
sound, followed by a second of a loud, rumbling nature, and 
lasting for a much longer period than the first report. The second 
report is usually followed by fire, destroying the plant and sur- 
rounding property. An explosive mixture, consisting of a very 
small quantity of fine dust in suspension, ignited by sufficient 
temperature would, no doubt, cause the sharp report usually 
heard first. This original ignition, possibly only an infiammation, 
would produce sufficient concussion to disturb the dust that is 
settled and packed on surrounding ledges and projections, and 
shake this fine dust into the air, making an additional explosive 
mixture. The heat, or flame from the original small puff, or 
inflammation, would cause an ignition of this newly formed mix- 
ture, and the explosion would propagate throughout a very large 
area, until the entire dust zone would be covered. This would 
probably account for the loud, rumbling sound of long duration, 
accompanied by a large body of flame. 

This establishes an important relation between the dust in a 
settled or packed condition and the amount of dust in suspension 
that is necessary to originate the explosion. Many theories and 
ideas have been advanced as to the conditions under which dust 
explosions are produced and the amount of dust in suspension 
necessary to originate the explosion, all probably based on differ- 
ent tests and experiments. It is generally agreed that the dust 
must be fine and dry, and in a state of suspension in the atmos- 
phere, which upon being brought in contact with sufficient heat 
or flame, causes an ignition. It is conceded that there must be a 
proper proportion in diffusion so that the explosive mixture of 
dust and air will ignite with sufficient force to propagate to an 
explosion. 

MEASURING DUST IN THE AIR 

It is especially important to devise some accurate manner in 
which the dust content of the air can be accurately determined. 
Steps have already been taken since this study began, to arrange 
an apparatus whereby dust samples could be collected from the 
air in mills and elevators, and the content per cubic foot, deter- 
mined. In this manner the efficiency of dust-collecting devices, 
sweeping systems, etc., can be determined by the analysis of the 
dust samples collected throughout the plant. When experiments 
have shown the amount of dust required to produce the original 



56 The Explosibility of Grain Dusts 



ignition, a system of this kind will detect the presence of a 
dangerous dust mixture, and show the quantity of dust in 
suspension. 

CAUSES OF GRAIN-DUST EXPLOSIONS 

The following causes have been assigned to many of the 
explosions in milling plants throughout this country and abroad: 

(1) Use of open lights, or naked flames, such as lamps, 
torches, gas jets, lanterns, candles, matches, etc. 

(2) Property fires. 

(3) Introduction of foreign material in grinding machines. 

(4) Electric sparks from motors, fuses, switches, lighting 
systems. 

(5) Static electricity produced by friction of pulleys and 
belts, grinding machines, etc. 

Use of Naked Lights 

At the present time in modern milling plants the use of an 
open flame is positively prohibited, and it is generally regarded as 
an element of very great danger to introduce an open flame into 
a dusty atmosphere. Many explosions in milling plants have 
been traced to this source, and it is a practice that cannot be too 
harshly condemned, and should be strongly prohibited. The use 
of gas jets for lighting purposes, the introduction of lanterns or 
open lights into grain bins or dust-collecting systems, and similar 
practices, are very dangerous, and should be discontinued at once. 

Property Fires 

Many violent explosions have occurred during mill fires, due 
to the presence of dust in large quantities. The flames and force 
from a fire produce sufficient concussion to jar the dust into sus- 
pension and initiate a very violent explosion. A plant where dust 
is allowed to accumulate in large quantities, and where steps are 
not taken to remove same as often as necessary, is always in 
danger of fires and explosions. 

Introduction of Foreign Material Into Grinding Machines 

A large number of explosions in more recent years have been 
traced to the introduction of foreign materials into grinding 
machines. Occurrences of this nature have been especially fre- 
quent in the grinding of oat hulls and feeds. Particles of foreign 



Prevention of Grain-Dust Explosions 57 

material seem to pass the separating systems and, coming in 
contact with the grinding plates of the machines, produce suf- 
ficient sparks to cause an ignition of the dusts in the grinding 
machines and conveyor lines. 

Electric Sparks from Motors, Fuses, Etc. 

Explosions have been assigned to the ignition of the dust 
cloud by an electric arc, and by sparks from motors, blown fuses, 
switchboards, starting boxes, lighting systems, etc. It has been 
thought that if a trip of mine cars should run away on a dusty 
road and break the trolley or feed wires, the electric arc produced 
may be sufficient to cause an ignition of the dust stirred up by 
the wrecking of the trip. As already stated, a disastrous explo- 
sion in Liverpool, England, in 1911, was due to the ignition of 
dust stirred up by the breaking of a belt. The cause of the 
ignition was assigned to sparks from a blown fuse of a temporary 
switchboard. 

Static Electricity 

The production of static electricity by friction of pulleys and 
belts has been assigned as the cause of recent dust explosions. 
Although experiments have not been conducted along this line to 
show that a dust cloud can be ignited in this manner, a recent 
experiment at Pittsburgh showed very clearly that sufficient 
static electricity could be produced by a very small pulley and 
shaft, to readily ignite gas. A Milling Company in Texas, engaged 
in grinding cottonseed cake into meal, states, that after experi- 
encing a series of explosions, the insulating of a certain grinding 
machine prevented any repetition of previous occurrences. The 
fact that explosions have been known to occur at times when the 
feed of grinding machines was cut off, seems to indicate that an 
unknown factor may be the responsible agent. A series of experi- 
ments are being planned in order to determine if static electricity, 
produced in this manner, can produce an ignition of the dust 
while in suspension. 

PREVENTION OF GRAIN-DUST EXPLOSIONS 

Presence of Foreign Materials in Grain 

Since only a very small quantity of dust in suspension is nec- 
essary to present conditions favorable to ignition, it would appear 
advisable that the proper thing to do would be to avoid the pro- 
duction or escape of dust into the atmosphere, as far as this is 



58 The Explosibility of Grain Dusts 

possible. From the large number of explosions thought to have 
been due to the presence of foreign material in the grain, it 
appears that the grain contains a portion of this material from 
the original point of shipment. During the transportation by 
boats, cars, etc., and also storage in the elevators, the quantity 
of foreign material is no doubt increased and suggests the impor- 
tance of cleaning the grain at the very first stages of handling. 
Much of the foreign material that causes trouble later on seems 
to originate in loading grain from the field. The quantity of 
foreign material present may be reduced by a cleaning process 
at the point of origin, and steps then taken to prevent the addi- 
tion of any further quantity of foreign material during trans- 
portation and handling. It appears to be a commercial problem, 
but should command consideration. 

Size of Receiving Bins 

In addition to the source of danger presented by hard foreign 
materials striking the plates of grinding machines, the size of 
the bins receiving ground material has an important relation to 
the extent of the fire or the violence of the explosion. If the bin 
is of large dimensions and very deep, it gives a very large area 
that may become filled with very fine dust in suspension. A 
number of violent explosions have occurred, due to a flame coming 
into contact with the suspended dust in bins containing only a 
small quantity of grain. 

Use of Portable Electric Lamps 

It is necessary in mills and elevators, for the workmen to 
determine at frequent intervals the amount of grain that the 
storage bins contain. A common practice is to lower a light 
of some kind into the bin, to observe or measure the quantity of 
grain. Many explosions have occurred when open lights and 
lanterns were introduced into grain bins for this purpose, and the 
practice cannot be too strongly condemned. The relation of the 
electric spark to the ignition of the dust cloud has not been fully 
determined by experiment, and many companies, for this reason, 
have discontinued the lowering of incandescent electric light bulbs 
into dusty atmospheres. There is a tendency for the workmen to 
become hasty in an effort to ascertain the quantity in series of 
bins, and the bulb may, by contact with the side of the bin or 
floor, become broken and introduce an element of possible danger. 



Prevention of Grain-Dust Explosions 59 



The desired result can be obtained by lowering a "tape" with a 
weight attached to the end, and the exact measurement can be 
recorded. 

When occasion renders it absolutely necessary to use a lamp 
of some kind in a bin an approved type of portable electric lamp 
could be used. The Electrical Section of the Bureau of Mines has 
recently approved three different types of lamps for safety in 
gaseous mixtures. Their value from a commercial standpoint as 
regards economy and efficiency still remains to be ascertained. 
Portable electric lamps are still in the early stages of perfection, 
and new types of lamps are being introduced on the market from 
time to time. 

Electric bulbs in dusty atmospheres located near machinery 
where there is a possibility of the lamp becoming broken, or at 
points in the mill where workmen may strike the lamp, especially 
when carrying a projection of some kind on their shoulder, should 
be enclosed in strong wire guards or protectors ; and it would be 
advisable also to enclose each bulb in a vapor-proof globe. An 
extra safety feature would be, whenever possible, to locate all 
fuses on light and power circuits, switches, starting boxes, 
motors, etc., at points where dust is not present in dangerous 
quantities. 



PRESS OF THE 

KEYSTONE Printing Company 

OF PITTSBURGH 



• ■qJ' 




















>- ./\>;^^\ oo\^;:>o ./\i.^/\ ^^^ 









,/ -O^^^^^O^ V^\^^' ^O.*^^/ ^/-- 






















ri^^ »■ 








^^-^o, 






* AT Oi 










^^^^ 




V<i- 






(^ vP^ -I 
























-^0^ 




'oV" 







^^0^ 




'^oV 



.^' 



e--^^ 



*". "- 





'\1 30 



I ^SSt^ INDIANA 46962 






• <^ 








0' 







